Glass Ionomers are prepared by mixing fluoride containing glass powders with aqueous solutions of polyacids such as polyacrylic acid (PAA). Inclusion of tartaric acid in the liquid improves the setting characteristics of glass ionomer cements at certain concentration ranges (Crisp and Wilson, 1976). Objectives: To test whether intimate mixing of ionomer glass powder with a small amount of dry polyacrylic acid (PAA) leads to higher compressive strength (CS) for the cement other factors being equal. This may occur via the formation of a partially neutralized PAA layer on the surface of the glass increasing the rate of reaction with leached ions from the glass when the aqueous phase is introduced by mixing. Methods: Aqueous solutions of polyacids containing 0, 1 and 5% tartaric acid were mixed either with ionomer glass or ionomer glass premixed with 5% PAA by weight. Work/set times (WT/ST) and CS were then measured. Results: As shown in the Table, inclusion of tartaric acid at the 5% level leads to higher CS for the ionomer glass alone but its effect on the CS is not significant when the glass is precoated with PAA. In all cases tested tartaric acid improves setting characteristics mostly by shortening set time.

% Tartaric acid	0		1		5
	WT/ST	CS (MPa)	WT/ST	CS (MPa)	WT/ST	CS (MPa)
Ionomer Glass only	2:30/5:45	101 (12)a	1:55/4:20	128 (12) a	2:35/5:25	160 (6)
Ionomer Glass + PAA	2:40/5:55	131 (32) b,d	1:40/4:00	140 (17) c,d	2:10/4:30	161 (9) b,c

Means with the same letter are not significantly different at p<0.05

Conclusions: The above results show that inclusion of tartaric acid in liquid improves setting properties of glass ionomer powders and increases CS although its effect on the CS for an ionomer glass already coated with PAA is less pronounced.

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